Steel Alloy, Use of Such a Steel Alloy, and Component

ABSTRACT

The invention relates to a steel alloy comprising, in percent by mass:—0.17 to 0.23 carbon;—1.40 to 1.60 silicon;—0.50 to 0.60 manganese;—up to 0.020 phosphor;—up to 0.020 sulfur;—up to 0.30 chrome;—up to 0.12 molybdenum;—up to 0.80 nickel;—up to 0.30 copper;—up to 0.03 vanadium; the remainder being iron and incidental impurities.

The invention relates to a steel alloy, a use of such a steel alloy, anda component.

Steel alloys such as, for example, G20Mn5 according to DIN EN 10293 arewell-known from the prior art.

It is an object of the present invention to provide a steel alloy, a useof such a steel alloy, as well as a component so that the component canbe manufactured from said steel alloy in a particular advantageous way.

This object is solved by a steel alloy having the features of patentclaim 1, by a use having the features of patent claim 4, and by acomponent having the features of patent claim 10. Advantageousembodiments of the invention are indicated in the dependent claims.

A first aspect of the present invention relates to a steel alloycomprising, in percent by mass, 0.17 to 0.23 carbon (C). The unit orspecification “percent by mass” is also referred to as “percentage bymass”, “percentage by weight”, “percent by weight”, “weight percent,“weight percentage” or “mass fraction”. In the context of the presentinvention, the percentage by mass of a substance within a mixture or analloy such as the steel alloy according to the present invention is theratio of the mass of that substance to the total mass of the mixture orthe alloy respectively. With respect to an alloy such as the steel alloyaccording to the present invention, said substance can be an alloyingelement such as carbon. In other words, said carbon is a substance ofthe steel alloy according to the present invention.

Furthermore, the steel alloy according to the present inventioncomprises, in percent by mass, 1.40 to 1.60 silicon (Si), 0.50 to 0.60manganese (Mn), up to 0.020 phosphor (P), up to 0.020 sulphur (S), up to0.30 chrome (Cr), up to 0.12 molybdenum (Mo), up to 0.80 nickel (Ni), upto 0.30 copper (Cu) and up to 0.03 vanadium (V), the remainder orbalance being iron (Fe) and incidental or unavoidable impurities. Thismeans the carbon, the silicon, the manganese, the phosphor, the sulphur,the chrome, the molybdenum, the nickel, the copper and the vanadium aresubstances, in particular alloying elements, of the steel alloyaccording to the present invention. Moreover, said iron and saidimpurities are substances of the steel alloy according to the presentinvention. Particularly, said impurities can be conditional ofmanufacturing. Preferably, the steel alloy according to the presentinvention comprises at least 90 percent by mass, in particular at least95 percent by mass and preferably at least 95.5 percent by mass of iron.Preferably, the steel alloy according to the present invention comprisesat least 95.78 percent by mass of iron. In other words, preferably, thesteel alloy comprises a mass fraction of at least 90 percent, inparticular at least 95 percent, preferably oat least 95.5 percent andpreferably at least 95.78 percent of iron, the remainder beingincidental or unavoidable or inevitable impurities.

It has surprisingly been found that the steel alloy according to thepresent invention can be processed, in particular cast, in a particularadvantageous way so that components can be made of the steel alloyaccording to the present invention in a particular advantageous, time-and cost efficient way. It has particularly been found that silicon, inparticular its mass fraction or percentage by mass according to thepresent invention, helps create a particularly good flowability of amolten mass made from the steel alloy according to the presentinvention. Moreover, the mass fraction of silicon according to thepresent invention helps realize an advantageously low solidustemperature. Furthermore, it has been found that manganese and its massfraction according to the present invention help avoid an excessive orunwished reactivity, in particular during processing the steel alloy.

In a particular advantageous embodiment of the invention, the steelalloy according to the present invention is a steel cast alloy. It hasbeen found that the steel alloy according to the present invention canbe cast in a particular advantageous way due to said substances andtheir respective mass fractions. In other words, the steel alloyaccording to the present invention can be processed particularadvantageously by casting.

In a further advantageous embodiment of the invention, the steel alloyas cast has a Brinell hardness of at least 190 HBW 5/750 and/or a yieldpoint (R_(p0.2)) of at least 300 megapascal (N/mm²). Thus, particularadvantageous characteristics of the steel alloy and, thus, a componentmade from the steel alloy can be realized.

A second aspect of the present invention relates to a use or usage ofthe steel alloy according to the present invention, wherein at least onecomponent is made from the steel alloy, in particular by casting, i.e.by a casting method or a casting process. In other words, the secondaspect of the present invention relates to a method for manufacturing atleast one component. In said method the component is manufactured ormade from the steel alloy according to the present invention.Preferably, in said method, the component is made from the steel alloyby casting, i.e. by a casting method or a casting process. Thus, thecomponent can be made in a particular easy and time- and cost-efficientway. In particular, a particularly low wall thickness of the componentcan be realized by manufacturing the component from the steel alloyaccording to the present invention. Advantages and advantageousembodiments of the first aspect of the present invention are to beregarded as advantages and advantageous embodiments of the second aspectof the present invention and vice versa.

In a particularly advantageous embodiment of the invention, thecomponent is subjected to a heat treatment after the casting. Forexample, the component is subjected to at least or exactly one heattreatment after the casting. Thus, particular advantageouscharacteristics of the component can be realized.

In a further advantageous embodiment of the invention, the heattreatment comprises a normalizing of the component. Preferably, the heattreatment is a normalizing of the component.

In order to realize particularly advantageous characteristics of thecomponent, in a further embodiment, the normalizing is carried out in atemperature range extending from 900 degrees centigrade to 980 degreescentigrade.

Preferably, after the heat treatment the steel alloy has a tensilestrength (R_(m)) of at least 560 megapascal and/or a yield point(R_(p0.2)) of at least 370 megapascal and/or an elongation at break(A_(5.65)) of at least 20% and/or a Vickers hardness of at least 180HV10 and/or a viscosity or ductility (KV) of at least 27 joule, whereinthe ductility has been or can be determined by an impact test. Saidtensile strength, said yield point, said elongation at break, saidductility and said Vickers hardness as well as said Brinell hardness aremechanical characteristics or properties of the steel alloy or thecomponent respectively, wherein said properties and their mentionedcharacteristic values have been or can be determined according to DIN ENISO 6892-1, in particular by means of a tensile test according to DIN ENISO 6892-1. Particularly, said properties and their mentionedcharacteristic values have been or can be determined by means of asample or probe which can be taken or drawn according to DIN EN ISO 377.The probe or sample is also referred to as a specimen. If possible, thespecimen type E according to DIN 50125 should be chosen. Particularly,the standards, in particular the DIN EN standards mentioned herein areor have been valid on Jun. 29, 2017.

In order to realize particularly advantageous characteristics of thesteel alloy or the component respectively, in a further advantageousembodiment of the invention, a homogeneous perlitic-ferritic structureor micro structure is created by the heat treatment, wherein during theheat treatment, a carbonization and a decarbonisation of the componentor steel alloy respectively are omitted.

A third aspect of the present invention relates to a component which is,preferably, a cast component. Said component is made from the steelalloy according to the invention, i.e. the steel alloy according to thefirst aspect of the present invention. Preferably, the component ismanufactured by means of said use or method for manufacturing thecomponent. Advantages and advantageous embodiments of the first andsecond aspects of the present invention are to be regarded as advantagesand advantageous embodiments of the third aspect of the presentinvention and vice versa.

Preferably, the component is a body component for a body in white or anintegral body of a vehicle, in particular a passenger vehicle. The bodyin white or the integral body are also referred to as a self-supportingbody, body work or shell. Preferably, the body component is a dome suchas a suspension-strut dome. In this regard, the dome has a particularlylow wall thickness which can be realized by using the steel alloyaccording to the present invention.

Further details of the invention derive from the following descriptionof preferred embodiments as well as from the drawings. The drawings showin:

FIG. 1 part of a schematic and perspective view of a component accordingto the present invention;

FIG. 2 part of a further schematic and perspective view of thecomponent; and

FIG. 3 a flow diagram illustrating a method for manufacturing thecomponent.

In the figures the same elements or elements having the same functionsare indicated by the same reference signs.

FIGS. 1 and 2 show a component 1 for a vehicle such as a car or anautomobile. In particular, said vehicle is a passenger vehicle having,in its completely assembled state, a body in white which is alsoreferred to as a body, an integral body, a self-supporting body, abodywork or a shell. In this regard, the component 1 is a body componentof the body in white. Particularly, the component 1 is a dome in a formof a suspension-strut dome of the body in white. The component 1 has aparticularly low wall thickness. Moreover, the component 1 has a ribstructure 2 stiffening the component 1. Moreover, preferably, thecomponent 1 is formed in one piece. In other words, the component isintegrally formed. As can be seen from FIGS. 1 and 2, the component 1has a recess 3 which is, preferably, a through opening. For example, aspring and/or damper element such as a suspension-strut can be supportedon the component 1 in the vertical direction of the vehicle upwardly.Alternatively or additionally, the spring and/or damper element can bearranged partially in the recess 3.

In order to manufacture the component 1 in a particular easy and time-and cost-efficient way the component 1 is made from a steel alloy bycasting, i.e. by a casting method. Said steel alloy is a steel castalloy which can be processed by casting in a particularly easy and time-and cost-efficient way. Said steel alloy comprises at least thefollowing substances, given in mass fractions in the unit %:

-   -   0.17 to 0.23 carbon (C)    -   1.40 to 1.60 silicon (Si)    -   0.50 to 0.60 manganese (Mn)    -   up to 0.020 phosphor (P)    -   up to 0.020 sulphur (S)    -   up to 0.30 chrome (Cr)    -   up to 0.12 molybdenum (Mo)    -   up to 0.80 nickel (Ni)    -   up to 0.30 copper (Cu)    -   up to 0.03 vanadium (V)    -   the remainder or balance being iron (Fe) and incidental,        unavoidable or inevitable impurities.

This means the steel alloy comprises the afore-mentioned substances, inpercent by mass or percentage by mass. In particular, due to the massfractions of silicon and manganese respectively, the steel alloy can beprocessed very well, in particular by casting.

Preferably, after casting the component 1, the component 1 is subjectedto a heat treatment, which is, preferably, a normalizing of thecomponent 1. The normalizing is also referred to as a normalization andshould be performed in a temperature range of 900 to 980 degreescentigrade. For example, the component 1 is normalized in an oven. Atemperature and an atmosphere in the oven during the normalizing shouldbe chosen in a way that a homogeneous perlitic-ferritic grain structureof the component 1 is accomplished and neither carbonisation nordecarbonisation of the component 1 or the steel alloy respectivelyoccurs. This can be proven by means of a grain structure analysis.

Preferably, in a state or condition after the heat treatment and beforean optional or possible further heat treatment to which the component 1is possibly subjected, the component 1 or the steel alloy has a tensilestrength (TS) of at least 560 megapascal and/or a yield point or yieldstrength (YS) of at least 370 megapascal and/or an elongation at breakor a fracture elongation (A_(5.65)) of at least 20 percent and/or atensile ductility or toughness (KV) of at least 27 joule and/or aVickers hardness of at least 180 HV10. A measurement to determine saidtoughness is preferably carried out according to ISO 148-1:2016 which,preferably, is or has been valid on Jun. 29, 2017. Alternatively oradditionally, a measurement for determining said hardness is carried outaccording to DIN EN ISO 6507-1. Said tensile strength, said yieldstrength, said fracture elongation, said toughness and said Vickershardness are mechanical properties or mechanical characteristics innormalized condition of the component 1, i.e. after said normalizing.

Preferably, after the casting and after the heat treatment the component1 is cleaned, preferably by centrifugal blasting. Preferably, thecomponent 1 is cleaned by means of airless blast cleaning after thecasting and after the heat treatment.

FIG. 3 shows a flow diagram illustrating a process or process sequencewhich is carried out after the casting and after the heat treatment and,preferably, after said cleaning of the component 1. The process sequenceshown in FIG. 3 is carried out in order to realize a particularly highquality of a surface of the, in particular completely manufactured,component 1.

In a first step S1 of the process sequence, the component 1 isdegreased, preferably by means of an alkaline fluid. In a second step S2the component 1 is subjected to a first purging in which, preferably,the component 1 is purged by means of deionised water. Preferably, thesecond step S2 is carried out after the first step S1. In a third stepS3 of the process sequence the component 1 is subjected to anultrasonically cleaning in which, preferably, the component 1 is cleanedby means of the deionised water. Preferably, the third step S3 iscarried out after the second step S2. In a fourth step S4 of the processsequence the component 1 is subjected to a first chemical polishingwhich is preferably carried out after the third step S3. In the fourthstep S4 at least or exactly one layer having a thickness of 10 to 15micrometres is abased from the component 1.

In a fifth step S5 the component 1 is subjected to a second chemicalpolishing. The fifth step S5 is an alternative to the fourth step S4 sothat either the fourth step S4 or the fifth step S5 is carried out. Inthe fifth step S5 at least or exactly one layer having a thickness of 25to 30 micrometres is abased from the component 1. Preferably, the fourthor fifth step respectively is carried out after the third step.

In a sixth step S6 which is preferably carried out after the fourth stepS4 or the fifth step S5 respectively, the component 1 is subjected to asecond purging in which the component 1 is purged by deionised water. Ina seventh step S7 of the process sequence the component 1 is subjectedto an ultrasonically cleaning, wherein, preferably, the seventh step S7is carried out after the sixth step S6. In the seventh step S7, thecomponent 1 is ultrasonically cleaned by means of deionised water. In aneighth step S8 of the process sequence the component 1 is subjected to apickling which is also referred to as a pickeling. Preferably, by meansof the pickling the component 1 is cleaned. Preferably, the eighth stepS8 is carried out after the seventh step S7.

In a ninth step S9 of the process sequence the component 1 is subjectedto a galvanising process in which the component 1 is galvanised.Preferably, the ninth step S9 is carried out after the eighth step S8.In the ninth step S9, the component 1 is furnished or provided with atleast one layer by means of galvanising. Said layer is made of zinc (Zn)in order to protect the component 1 from corrosion. Since thegalvanising in the ninth step S9 is carried out after the picklingcarried out in the eighth step S8, the layer adheres particularlyadvantageously or strongly to the surface of the component 1. In otherwords, by means of the pickling carried out in the eighth step aparticularly advantageous surface of the component 1 can be realized,wherein the layer created in the galvanising process carried out in theninth step S9 can adhere very advantageously and strongly to saidsurface created by the pickling.

In a tenth step S10 of the process sequence the component 1 is providedwith a corrosion protection oil, in particular by spraying. In otherwords, in particular and preferably, said corrosion protection oil issprayed on said zinc layer and, thus, on a surface formed by said layerwhich is a zinc layer. Preferably, the tenth step S10 is carried outafter the ninth step S9.

Preferably, the component 1, in particular in its completelymanufactured state, has a surface having a surface roughness fulfillingthe following demands: Ra max. 10 micrometres, Rz max. 50 micrometresand Rt max. 75 micrometres. Preferably, said surface roughness isdetermined or measured according to DIN EN ISO 4288:1997.

The ninth step S9 is a coating or coating process which is also referredto as a galvanic zinc coating or galvanic zinc coating process, saidlayer being a zinc layer is a coat or a zinc coat. The zinc coat is alsoreferred to as a sink coating which is, preferably, at every position ofthe component 1 and, thus, completely closed. Preferably, the layer hasa thickness of 7 to 15 micrometres.

LIST OF REFERENCE SIGNS

-   1 component-   2 rip structure-   3 recess-   S1 first step-   S2 second step-   S3 third step-   S4 fourth step-   S5 fifth step-   S6 sixth step-   S7 seventh step-   S8 eighth step-   S9 ninth step-   S10 tenth step

1. A steel alloy comprising, in percent by mass: 0.17 to 0.23 carbon;1.40 to 1.60 silicon; 0.50 to 0.60 manganese; up to 0.020 phosphor; upto 0.020 sulfur; up to 0.30 chrome; up to 0.12 molybdenum; up to 0.80nickel; up to 0.30 copper; up to 0.03 vanadium; the remainder being ironand incidental impurities.
 2. The steel alloy according to claim 1,wherein the steel alloy is a steel cast alloy.
 3. The steel alloyaccording to claim 2, wherein the steel alloy as cast has a Brinellhardness of at least 190 HBW 5/750 and/or a yield point of at least 300megapascal.
 4. A method of manufacturing an article, the methodcomprising casting the steel alloy according to claim 1 to form thearticle.
 5. The method of claim 4, further comprising subjecting thearticle to a heat treatment after casting.
 6. The method of claim 5,wherein the heat treatment comprises a normalizing of the article. 7.The method of claim 6, wherein the normalizing is carried out in atemperature range extending from 900 degrees centigrade to 980 degreescentigrade.
 8. The method of claim 5, wherein after the heat treatmentthe steel alloy has a tensile strength of at least 560 megapascal and/ora yield point of at least 370 megapsacal and/or an elongation at breakof at least 20% and/or a Vickers hardness of at least 180 HV10 and/or atensile ductility of at least 27 joule.
 9. The method of claim 5,wherein the heat treatment creates a homogeneous perlitic-ferriticstructure and during the heat treatment a carbonization and adecarbonization of the article are omitted.
 10. A component of avehicle, the component cast from a steel alloy according to claim
 1. 11.The component of claim 10, wherein the component is a body component fora body in white or an integral body of a vehicle.
 12. The component ofclaim 11, wherein the body component is a dome.